Services paid for in advance, particularly services in a data or telecommunication system, are also known as prepaid services, an electronic credit being built up with a service provider e.g. by means of cashless transfer or cash purchase of a telephone card (prepaid card) by the user. The service provider's services booked in this manner can then be selected cashlessly by the user from any touch-tone telephone, from a telephone booth, in a hotel etc. via a toll-free service number and used e.g. by entering a user ID. Services of this kind can also be used from a mobile telephone, correspondingly attractive tariff plans being possible for the service operators through pre-payment of the service charges. Generally tariff models tailored to the user's requirements are provided, e.g. for the preferred use of international or national connections, local or long-distance calls, etc.
The scope of the services offered extends not only to voice communication using fixed or mobile telephones, but also to text-based communication services such as e-mail or SMS (Short Message Service). In addition, services such as voice mail (answering machine function), Internet access (WAP phone, Internet computer) or reduced-rate services such as travel information, telephone information etc. can be provided. The advantages of using a service package of this kind have so far resulted in an increasing number of users. However, the disadvantage of the present system is that, if credit runs out while a service is being used, the line is cut off which means that it is no longer possible for the user to top off his credit in good time. This is all the more unacceptable for the user in that cut-off may occur while an important service is being used, e.g. an important international call, and can have serious consequences.